Soil conservation management with cover crops: effects on critical energy levels, release and dispersion of aggregates
ABSTRACT The normalized dispersion index (NDI) and the b/a index are commonly used to express the stability of aggregates measured by ultrasound. However, few studies have used the critical energy (CE) extracted from modeling to explain the effects of soil use and management on soil aggregation. The objective of this study was to evaluate the influence of soil cover on the CE level required for dispersion of aggregates of a Typic Hapludalf. Soil samples collected from the 0.0-0.05 m depth were evaluated in five different managements with cover plants: perennial soybean (PS), peanuts (P), spontaneous vegetation (SV), black oat/forage turnip (BOFT), and black oat/hairy vetch (BOHV). Aggregates ? 2 mm of the treatments were exposed to ultrasonic irradiation during 0, 30, 60, 120 and 180 s. The specific applied energies were calculated based on sonification time and potency: 0, 745, 1490, 2980, and 4470 J·g–1. After each sonification, sand (2000-53 ?m), silt (53-2 ?m) and clay (< 2 ?m) were quantified. The mass of aggregates of each size class was modeled as a function of the ultrasonic energy. The CE, the NDI and the b/a indexes were coefficients extracted from these models. Cover crops influenced the critical energy levels required for dispersion of aggregates of the Typic Hapludalf. However, our methodology did not prove management systems with intercrops of the cover crops, as black oats and vetch, contribute more effectively to the increase of soil aggregation.